The present invention relates to the field of plasma treatment, in particular to a method and apparatus for treating various surfaces with improved uniformity of treatment. The invention may find application in such operations as etching, activation, cleaning, deposition, etc., in particular for treating surfaces of substrates in the manufacture of semiconductor devices.
The problem of uniformity of surface treatment in the semiconductor manufacturing remains important and even becomes more aggravated with development of new generations of semiconductor manufacturing machines, in particular with the transfer to 300 mm diameter wafers. For example, if in the previous generation of semiconductor manufacturing machines 5 to 3% uniformity of plasma treatment was acceptable, the modern machines for wafers of 300 mm in diameter should guarantee non-uniformity of plasma treatment not exceeding 2%.
Many attempts have been made heretofore to solve the problem of process uniformity in plasma treatment. All these attempts can be roughly divided into methods and devices based on redistribution of plasma-excitation electromagnetic fields and methods and devices based on movements or oscillations of the objects during plasma treatment.
For example, U.S. Pat. No. 4,840,702 issued in 1989 to Schumacher, III; John E. discloses a typical apparatus and method for improved plasma treatment of circuit boards in a plasma-treating zone and in a gas resupply zone established in a working chamber. The apparatus is provided with an actuating mechanism for causing a relative movement between the circuit boards and the zones where the boards are treated. The apparatus preferably includes a chamber for receipt of a gas and has electrodes centrally positioned therein for generating an electrical field at a central portion of the chamber thereby exciting the gas there and creating a zone of intense plasma. A transport mechanism is provided in the chamber for moving the circuit boards alternately into and out of the central portion of the chamber for preselected periods of time thus alternately exposing the circuit boards to the intense plasma and to substantially fresh gas outside of the central portion of the chamber thereby providing more uniform plasma treatment of the surface areas of the circuit boards and improved cleaning and etching of openings through the circuit boards which receive a fresh supply of gas therein when the circuit boards are outside of the central portion of the chamber. Using appropriate electrodes, the same apparatus may be employed for deposition of metallic layers on the boards in a substantially continuous operation after plasma treatment.
The construction of the type described above was typically employed in conveyor-type systems, e.g., in systems for treating hard-drive disks in multiple-station conveyor type machines. Such plasma treatment devices are intended for use in specific machines and lack versatility required for modern stand-alone or cluster-type machines.
Known in the art are also ion-beam plasma treatment systems with rotation of the substrates with respect to the treatment beam. An example of such an apparatus is a device described in U.S. Pat. No. 6,238,582 issued on May 29, 2001 to K. Williams, et al. Although the apparatus of U.S. Pat. No. 6,238,582 relates to a reactive ion beam etching method, other than to the systems with anizotropic RF plasma, the principle used for achieving uniformity may serve as a typical example of an apparatus in which the uniformity is achieved by rotating the substrate with respect to the treating beam. More specifically, a process chamber of this apparatus includes a substrate holder that is pivotally mounted such that the angle of incidence of a collimated ion beam relative to a normal to the substrate surface may be adjusted in situ (i.e., during a process, without breaking vacuum). The substrate holder may be implemented for holding and rotating a single substrate, or for holding and moving two or more substrates in, for example, a planetary motion.
There are many other substrate treatment systems similar in principle, such as magnetron sputtering, ion-beam treatment, ion-beam sputtering, electron-beam sputtering, etc., where uniformity of treatment is achieved by rotating or otherwise moving the substrate with respect to the processing beam during treatment.
The second aforementioned method, which is less popular, is redistribution of electromagnetic plasma-excitation fields during treatment. A good example of such a system is the Endura system produced by Applied Materials, Inc. In this machine, which is described, e.g., in U.S. Pat. No. 6,297,595 issued on Oct. 2, 2001 to B. Stimson, improved uniformity is achieved by utilizing two 13.72 MHz RF antennas instead of one. Superposition of the electromagnetic plasma-excitation fields produces more uniform distribution of the resulting field in a space above the treated substrate.
Another approach to the solution of the uniformity treatment problem is to improve the design and parameters of the plasma-excitation coils or to use several coils.
For example, U.S. Pat. No. 4,948,458 issued to J. Ogle in 1990 discloses a multi-turn spiral coil for achieving improved uniformity. The spiral element, which is generally of the Archimedes type, extends radially and circumferentially between its interior and exterior terminals connected to the RF source via an impedance matching network. Coils of this general type produce oscillating RF fields having magnetic and capacitive field components that propagate through the dielectric window to heat electrons in the gas in a portion of the plasma in the chamber close to the window. The oscillating RF fields induce in the plasma currents that heat electrons in the plasma. The spatial distribution of the magnetic field in the plasma portion close to the window is a function of the sum of individual magnetic field components produced by each turn of the coil. The magnetic field component produced by each of the turns is a function of the magnitude of RF current in each turn, which differs for different turns because of transmission line effects of the coil at the frequency of the RF source.
For spiral designs as disclosed by and based on the Ogle ""458 patent, the RF currents in the spiral coil are distributed to produce a torroidal shaped magnetic field region in the portion of the plasma close to the window, where power is absorbed by the gas to excite the gas to a plasma. At low pressures, in the 1.0 to 10 mTorr range, diffusion of the plasma from the ring shaped region produces plasma density peaks just above the workpiece in central and peripheral portions of the chamber, so the peak densities of the ions and electrons which process the workpiece are in proximity to the workpiece center line and workpiece periphery. At intermediate pressure ranges, in the 10 to 100-mTorr range, gas phase collisions of electrons, ions, and neutrons in the plasma prevent substantial diffusion of the plasma charged particles outside of the torroidal region. As a result, there is a relatively high plasma flux in a ring-like region of the workpiece but low plasma fluxes in the center and peripheral workpiece portions.
These differing operating conditions result in substantially large plasma flux (i.e., plasma density) variations between the ring and the volumes inside and outside of the ring, resulting in a substantial standard deviation, i.e., in excess of three, of the plasma flux incident on the workpiece. The substantial standard deviation of the plasma flux incident on the workpiece has a tendency to cause non-uniform workpiece processing, i.e., different portions of the workpiece are etched to different extents and/or have different amounts of molecules deposited on them.
Many coils have been designed to improve the uniformity of the plasma. U.S. Pat. No. 5,759,280, Holland et al., issued Jun. 2, 1998, discloses a coil, which, in the commercial embodiment, has a diameter of 12 inches and is operated in conjunction with a vacuum chamber having a 14.0-inch inner wall circular diameter. The coil applies magnetic and electric fields to the chamber interior via a quartz window having a 14.7-inch diameter and 0.8 inch uniform thickness. Circular semiconductor wafer workpieces are positioned on a workpiece holder about 4.7 inches below a bottom face of the window so the center of each workpiece is coincident with a centerline of the coil.
The coil of the ""280 patent produces considerably smaller plasma flux variations across the workpiece than the coil of the ""458 patent. The standard deviation of the plasma flux produced by the coil of the ""280 patent on a 200 mm wafer in such a chamber operating at 5 milliTorr is about 2.0, a considerable improvement over the standard deviation of approximately 3.0 for a coil of the ""458 patent operating under the same conditions. The coil of the ""280 patent causes the magnetic field to be such that the plasma density in the center of the workpiece is greater than in an intermediate part of the workpiece, which in turn exceeds the plasma density in the periphery of the workpiece. The plasma density variations in the different portions of the chamber for the coil of the ""280 patent are much smaller than those of the coil of the ""458 patent for the same operating conditions as produce the lower standard deviation.
Other arrangements directed to improving the uniformity of the plasma density incident on a workpiece have also concentrated on geometric principles, usually concerning coil geometry. See, e.g., U.S. Pat. Nos. 5,304,279, 5,277,751, etc.
The problems inherent in apparatuses where uniformity of plasma treatment is achieved due to improvement in the construction of the coil and distribution of the plasma-excitation field are partially solved by a y system described in U.S. Pat. No. 6,319,355 issued on Nov. 20, 2001 to J. Holland. The apparatus utilizes an RF processor for treating workpieces with an RF plasma in a vacuum chamber and includes a coil responsive to an RF source to produce magnetic and electric fields that excite ionizable gas in the chamber to a plasma. Usually the coil is on or adjacent to a dielectric window that extends in a direction generally parallel to a planar horizontally extending surface of the processed workpiece. The excited plasma interacts with the workpiece in the chamber to etch the workpiece or to deposit material on it. The workpiece is typically a semiconductor wafer having a planar circular surface or a solid dielectric plate, e.g., a rectangular glass substrate used in flat panel displays, or a metal plate.
Although the last-mentioned device results in a rather high uniformity of treatment, a disadvantage of this device, as well as all other known devices, systems and methods mentioned earlier, consists in that uniformity of plasma treatment can be adjusted or controlled in a narrow range of RF power. None of the known devices and methods possesses versatility required for achieving uniformity required for plasma treatment of modern 300 mm diameter wafers, or similar products.
In some applications, e.g., for high-speed and heavy-duty etching of silicon and silicon oxides in fluorocarbonaceous gases, the plasma should have a very high density of electrons, e.g., higher that 1012 cmxe2x88x923. None of the existing technologies described above is capable of satisfying this condition.
It is an object of the present invention to provide an apparatus and method for uniform plasma treatment of surfaces of objects in a working chamber due to oscillations of the plasma-excitation electromagnetic field with respect to the treated surface. It is another object is to provide the aforementioned apparatus and method in which uniformity of plasma treatment is achieved by combining oscillatory movements of the plasma-excitation electromagnetic field with a running wave in a microwave frequency range. Still another object is to provide the apparatus of the last-mentioned type, in which the dielectric waveguide for microwaves is simultaneously used for the supply of cooling air. Another object is to provide the aforementioned apparatus, which is simple in construction and inexpensive to manufacture. Another object is to provide a method for improving uniformity of plasma treatment in surface treatment of objects such as semiconductor substrates. It is another object to provide an apparatus suitable for generating high-density plasma required for high-speed and heavy-duty etching of silicon and silicon oxides in fluorocarbonaceous media.